Thermostatic switch



Jui? 3, 1956 c. s. MERTLER 2,753,422

THERMOSTATIC SWITCH Filed March 11, 1953 Arroz/v5 YS United StatesPatent C THERMOSTA'HC SWITCH Charles S. Mertler, Mansfield, Ghia,assigner to Stevens Manufacturing Company, inc., Mansfield, lrio, acorporation of hio Application March 11, 1953, Serial No. 341,754

7 Claims. {CL 20d- 133) This invention relates to thermostatic switchesand, more particularly, to such switches in which contact operation iseffected in response to the reversal of curvature of a curved bimetallicdisc.

One type of thermostatic switch employs a curved bimetallic member inthe form of a substantially dishshaped or conveXo-concave disc as theoperating element. Such a disc snaps through center, i. e., rapidlyreverses its curvature, upon attaining a predetermined temperature andthis reversal of curvature is utilized to control the movement of acontact or contacts of the switch so that such movement is effected witha snap action. However, in prior switches of this type, it is customaryto firmly clamp the periphery or the central portion of the bimetallicdisc. Also, it is common in such switches to connect the movable contactmeans or a motion transmitting member to the bimetallic disc. Suchclamping of the disc or connection of members thereto destroys orgreatly reduces the ability of the disc to flex in the region of theclamping or connections, and hence the response of the disc totemperature changes is altered by the restraints thus imparted so thatthe switch operation tends to be erratic and/ or requires acomparatively large temperature differential. Moreover, the adjustmentor calibration of such switches has frequently been effected by meanswhich so alters the forces exerted upon the disc that the temperaturedifferential of the switch or other operating characteristics arealtered.

An object of this invention is to provide an improved snap actingthermostatic switch employing a curved bimetallic disc to controlcontact operation in which the disc has no portion thereof rigidly heldfrom movement and has no parts of the switch mechanism connected to thedisc so that the flexure of the latter is substantially unaltered by itsutilization in the switch mechanism thereby facilitating quantityproduction of switches having substantially uniform characteristics.

Another object of the invention is to provide an improved snap actingthermostatic Switch employing a curved bimetallic disc to controlcontact operation wherein the disc is loosely supported adjacent itsperiphery and the motion resulting from reversal of its curvature inresponse to a predetermined temperature is transmitted to a movablecontact member of the switch by a motion transmitting means which isresiliently maintained in abutting contact with the central portion ofthe disc but is not connected thereto whereby all areas of the disc arefree to respond to a predetermined change in temperature.

A further object of the invention is to provide an improved thermostaticswitch as defined in the preceding paragraphs and in which the motiontransmitting means between the bimetallic disc and movable conductivemember of the switch is carried by the latter and is adjustable relativethereto for conditioning the switch to operate at differentpredetermined temperatures.

An additional object of the invention is to provide an improved snapacting thermostatic switch as defined above wherein creepage or likelost motion of the bimetallic operating disc may be eliminated, therebypreventing frying of the contacts, without affecting the uniformity ofresponse of the switch upon attainment of a predetermined temperature.

A more specific object of the invention is to provide an improvedthermostatic switch as defined above wherein a movable contact member iscontinuously urged from engagement with stationary contact means of theswitch and carries a member adjustable relative to the movable contactmember and maintained in abutment with the central portion of aconveXo-concave bimetallic disc Jhich has the peripheral portion thereoffreely resting upon a planar surface, whereby the exure of the disc issubstantially unrestrained and hence switch operations in response toattainment of a predetermined temperature are substantially uniform.

The invention further resides in certain novel features of theconstruction and in combination of parts of the mechanism in which theinvention is embodied, and further objects and advantages of theinvention will be apparent to those skilled in the art to which itpertains from the following description of the presently preferredembodiment thereof which is described with reference to the accompanyingdrawing, forming a part of this application, and in which:

Fig. l is an enlarged top plan view of a therrnostatic switchconstructed in accordance with the invention, portions of the switchterminals being broken away; and

Fig. 2 is a vertical sectional view through the switch shown in Fig. l,the view being taken substantially on the sectional indicating line 2 2of Fig. l.

The embodiment of the invention in a snap acting thermostatic switch ishere illustrated as comprising a support including a base portion and aside wall portion 11. As here shown, the base 1i) is circular and formedof insulating material, while the side wall 11 is formed of metal,shaped to a substantially cylindrical configuration, and attached to thebase 10 by having spaced portions adjacent one edge removed therebyproviding integral projecting parts or lips 12 which are received incomplementary recess of the base lil and held in engagement therewith byan upsetting or spinning action performed upon the portions 12 as willbe readily understood by those skilled in the art. Alternatively, theside wall 11 may be formed integrally with the base 10.

The outer face of the base lll is provided with terminal members 13 and14, only a portion of which are here illustrated, but which may be ofany suitable form, the inner ends of which are received in recesses of aboss 15 on the base thereby preventing the terminals from contacting asurface which the base may engage. The terminals 13 and 14 are hereshown as secured to the base 12 by studs or rivets 16 and 17,respectively, the inner ends of which are enlarged and disposed upon theinner face of the base 1t) to thereby provide spaced stationary contacts18 and 19. The reduced diameter portions of the studs or rivets extendthrough aligned openings in the base and terminal members 13 and 14 withthe outer ends of these studs or rivets peened or upset on the outersurface of the terminal members thereby securing the latter to the haseas well as firmly holding the contacts 18 and 19 in place.

The movable conductive member of the switch is formed by a substantiallydisc-shaped member 20 of metal which is adapted to move to and frombridging engagement with the stationary contacts 1S and 19. As hereshown, the surface of the member 20, which engages the stationarycontacts 18 and 19, is provided with a layer 21 of silver or othersuitable Contact material but it will be understood that the member maybe formed of but a single material, if desired.

The member 20 has a central opening therethrough the side of the baseinternally of the side wall il, as is` indicated at 25, therebyproviding a seat for one end of a helical compression spring 26. Theother end portion of the spring is disposed around the adjacent end ofthe motion transmitting means 22 and engages the surface of theconductive member 2li.

The side wall 11 of the switch is provided with a planar surface 27facing towards the base i9, which surtace is here shown as provided uponan annular tiange 2b extending radially inwardly of the side wall lradjacent the outer edge thereof. The planar surface 27 provides thesupport for the peripheral portion of a dished bimetallic disc 29, whichis preferably imperforate and of convexoconcave shape, the centralportion of the disc being engagedby the adjacent end of the motiontransmitting7 means 22. Preferably, the motion transmission means 22 hasthe threaded portion 3@ formed of metal and provided with an axial borein which is received a headed stud or button 3l formed of insulatingmaterial, such as a ceramic substance or the like. The outer surface ofthe stud 3i, which is maintained in engagement with the bimetallic disc29, is preferably of convex coniiguration, as will be apparent from Fig.2, to lessen the area of contact.

A switch constructed as illustrated and described is of the normallyclosed type since the movable conductive member 2t? is normally held inengagement with the stationary contacts 1S and i9. However, when theswitch has been subjected to a predetermined temperature change, thebimetallic disc 29 will reverse its direction of curvature with a snapaction. Since the motion transmitting means Z2, carried by theconductive member or disc 2b, is maintained in engagement with thebimetallic disc 29 under the force of the spring 26, the member 20 ismoved from engagement with the contacts 1S and i9 by the spring 25 sothat the circuit through the switch is broken. The breaking of thecircuit is, therefore, positive in nature and rapidly effected undercontrol of the bimetallic disc 29. When the temperature to which theswitch is subjected returns to its initial value, the bimetallic disc 29will again reverse its curvature returning to the position illustratedin Fig. 2. This returns to movable conductive member 2@ into bridgingengagement with the contacts l and i9 thereby reclosing the circuitthrough the switch.

The temperature at which switch operation is effected may be adjusted,for calibration or like purposes, by altering the position of the motiontransmitting means 22 relative to the conductive disc or member 20. Thismay be eected after the switch is assembled by means of a screw driveror other suitable tool inserted through the opening 24 and engaged inthe slot 23 of the conductive member Ztl. Rotation of the member 2t?with the member 22 during such adjustment is prevented by one or moreguide members or studs 32 supported by the base l() and received insuitable recesses or openings in the periphery of the member 2b. Theseguide members or studs 32, which also serve to prevent radialdisplacement of the member 29, may be formed as integral portions on theinner face of the base lil or may be separate members secured thereto,if desired. Alternatively, the member 2@ may have a diameter closelyapproximating the interior diameter of the side wall ll and rotationpreventing cooperating surfaces provided upon the member 2b and theadjacent portion of the side wall 11. Furthermore, it is not necessarythat the member 2t) be a circular disc and hence this member and thecooperating rotation preventing means may be provided in other shapesand forms than those here specifically mentioned.

The adjusted position of the motion transmitting means 22 relative tothe conductive member 2t) may be maintained in any desired manner as,for example, by providing a small drop of solder between the means Z2and the member 2@ or by providing a locking action between the threadsof the member 2t) and the threaded portion 30 of the motion transmittingmeans. Such locking action may be achieved by forming one of the threadswith a slightly different pitch from that of the other thread or byother expediente well known in the art.

it will non' be apparent that, in accordance with this invention, thebimetallic disc 29 is free to flex in all portions thereof since it isneither clamped in place nor does it have any rigid members connectedthereto. Thus, it will be observed that the peripheral portion of thedisc freely rests upon the planar surface 27 and may slide slightlythereon to the extent necessary during ilexing of the disc when itreverses its direction of curvature. It wiil also be observed that themotion of the central portion of the disc is transmitted to the movableconductive member 2t? without the need of a connection to the disc sothat there are no holes in the disc or rigid members connected theretowhich would alter the mode of exing of the disc. Consequently, switchesof the type here disclosed can be produced in quantity with highlyuniform characteristics thereby reducing the amount of calibration oradjustment necessary to enable the switches to operate upon attaining adesired temperature. Furthermore, the temperature differential withinwhich the switches are operative is smaller and more nearly constantthan in the case of switches wherein the bimetallic disc is eitherclamped in place or has rigid connections thereto. in addition, it willbe observed that calibration of the improved switch may be readilyeffected after the switch is assembled and that this calibration doesnot alter the characteristics of the switch other than the temperatureto which it responds.

The adjustability provided by the threaded connection between themembers it? and 22 also permits elimination of contact frying byremoving creepage of the bimetallic disc. That is to say, when anunrestrained convexo-concave bimetallic disc is subjected to atemperature change the lirst response is a relatively slow increase inthe radius of curvature of the disc and the snap action does not occuruntil Va critical point is reached whereupon the disc snaps throughcenter. This relatively slow change of temperature, which is known ascreepage, frequently results in contact frying since the contactpressure is reduced by the creepage to the place where slightvibrations, jolts or the like will cause momentary separation of themovable Contact from the stationary contacts. This diiiculty may beeliminated with switches of the construction here disclosed by effectingadjustment of member 22 relative to the member 2i) until the formerengages the bimetallic disc 24 with sufficient force so that the latteris deflected an amount substantially corresponding to the aforementionedcreepage change in curvature. Consequently, the rst movement of abimetallic disc thus conditioned is a reversal of curvature, whichoccurs with a snap action, and there is no unstable position wherein thecontacts can intermittently open and close due to Vibrations or similardisturbances. l

Although the presently preferred embodiment of a switch constructed inaccordance with this invention has been illustrated and described inconsiderable detail, it is to be noted that these details of theconstruction may be altered by those skilled in the art withoutdeparting from the principles of the invention. For example, asmentioned above, the side wall and base may be formed in one piece. Inthe event such one piece construction employs metal as the material,insulating means for the terminals 13 and i4 and stationary contacts 18and 19 would, of course, be provided. Also, in the event the side walland base are formed in one piece, the planar surface for supporting thebimetallic disc 29 could then be formed either as a separable member orby spinning or otherwise turning inwardly a portion of the side wall 11after the bimetallic disc 29 is introduced therein. It will also beevident that although a layer of contact material 21 has been shown uponthe surface of the member 20, this layer may be omitted in certain casesand/or a similar layer of material could be provided upon the stationarycontacts 18 and 19. Furthermore, the shape of the conductive member 20may be other than a disc.

The aforementioned suggested changes in the construction are notexhaustive and are offered only as representative of alterations whichmay be made by those skilled in the art without departing from theprinciples of the invention. Consequently, it will be apparent that theinvention should not be construed as limited to the precise details ofstructure here illustrated and described except as may be required bythe subjoined claims.

Having thus described the invention, I claim:

l. A thermostatic switch unit comprising a base, a plurality ofstationary contacts on said base, a rigid conductive member movable toand from bridging engagement with said contacts, spring means betweensaid base and conductive member continuously urging the latter fromengagement with said contacts, a dished bimetallic disc adapted toreverse its direction of curvature upon attaining a predeterminedtemperature and having an imperforate central portion, means connectedto said base and forming therewith a switch housing enclosing saidconductive member and loosely supporting said disc adjacnt itsperiphery, and motion transmitting means adjustably secured to saidconductive member and having a portion abutting the central of said discwith a free bearing engagement, whereby operation of said switch may bevaried by adjusting the position of said motion transmitting meansrelative to said conductive member.

2. A thermostatic switch unit comprising a switch housing including asubstantially planar base portion and a side wall extending outwardlyfrom said base portion adjacent the periphery thereof, a plurality ofstationary electrical contacts mounted on said base portion within theconines of said side wall, a rigid electrical conductive member withinsaid housing and movable to and from bridging engagement with saidcontacts, spring means between said base portion and said conductivemember continuously urging the latter from engagement with saidstationary contacts, means extending inwardly of said side wall andspaced axially from said base portion providing a supporting surface onthe opposite side of said conductive member from said spring means, adished bimetallic disc having its peripheral portion freely resting uponsaid surface and its central portion imperforate and unsupported, andmotion transmitting means adjustably secured to said conductive memberand continuously abutting the central portion of said disc under theinfluence of said spring means with a free bearing engagement, wherebysaid conductive means is moved from engagement with said contacts bysaid spring means when said disc reverses its curvature and theoperation of the switch may be varied by adjusting the position of saidmotion transmitting means relative to said conductive member.

3. A thermostatic switch unit comprising a switch housing including abase having an opening therethrough and a side wall extending outwardlyfrom said base adjacent the periphery thereof, stationary electricalcontact means mounted on said base within the confines of said sidewall, a rigid conductive member Within said housing and movable to andfrom engagement with said contact means, the said housing also includinga planar surface facing said base and spaced axially therefrom on theopposite side of said conductive member from said contact means, aconvexe-concave bimetallic disc having its peripheral portion freelyresting upon said planar surface and its central portion unsupported,motion transmitting means adjustably secured to said conductive memberin alignment with the said opening in the base thereby per-.

mitting access to said means through said opening, the said motiontransmitting means abutting the central portion of said disc, and springmeans between said base and conductive member continuously urging theconductive member from engagement with the stationary contact means,whereby the said conductive member is moved from engagement with saidcontact means by said spring means when the bimetallic disc reverses itscurvature and the operation of the switch is adjusted by altering theposition of said motion transmitting means relative to said conductivemember.

4. A thermostatic switch unit comprising a base having a substantiallyplanar central opening, a side wall extending outwardly from said baseadjacent the periphery thereof and forming a switch housing therewith, aplurality of stationary contacts mounted on said base within thecontines of said side wall, a rigid conductive member within saidhousing and movable to and from bridging engagement with said contacts,means on said side wall providing a planar surface facing said base andspaced axially therefrom on the opposite side of said conductive memberfrom said contacts, a convexo-concave bimetallic disc having itsperipheral portion freely resting upon said planar surface and itscentral portion unsupported, motion transmitting means adjustablysecured to said conductive member in alignment with the said opening inthe base thereby permitting access to said means through said opening,the said motion transmitting means abutting the central portion of saiddisc, and spring means between said base and conductive membercontinuously urging the conductive member from engagement with thestationary contacts, whereby the said conductive member is moved fromengagement with said contacts by said spring means when the bimetallicdisc reverses its curvature, and the operation of the switch is adjustedby altering the position of said motion transmitting means relative tosaid conductive member.

5. A thermostatic switch comprising a base having a two-diameter centralopening, a side wall extending outwardly from said base adjacent theperiphery thereof on the side thereof having the portion of the openingwith the greater diameter, a plurality of stationary contacts mounted onsaid base within the contines of said side wall, a rigid conductivemember movable to and from bridging engagement with said contacts, anannular flange extending around the interior of said side wall providinga planar surface facing said base and spaced axially therefrom, aconvexo-concavo bimetallic disc having its peripheral portion freelyresting upon said planar surface and its central portion unsupported,motion transmitting means adjustably secured to said conductive memberin alignment with the said opening in the base thereby permitting accessto said means through said opening, the said motion transmitting meansabutting the central portion of said disc with a part of said motiontransmitting means extending beyond the conductive member on the sidethereof adjacent said base, and a helical spring having one end receivedabout the said extending portion of the motion transmitting means andthe other end received in the greater diameter portion of the opening insaid base thereby continuously urging the conductive member fromengagement with the stationary contacts, whereby the said conductivemember is moved from engagement with said contacts by said spring whenthe bimetallic disc reverses its curvature and the operation of theswitch is adjusted by altering the position or said motion transmittingmeans relative to said conductive member.

6. A switch as defined in claim 5 and wherein the adjustable connectionbetween said motion transmitting means and said conductive membercomprise interengaging screw threads, and the said motion transmittingmeans has a tool receiving surface on the portion thereof accessiblethrough said opening.

7. A switch as dened in claim 6 wherein the said motion transmittingmeans is an externally threaded member threaded through a tapped openingin said conductive member with portions extending on either side of saidconductive member, the end of said threaded member References Cited inthe le of this patent abutting said disc having a convex surface and theother l0 2,508,991

end thereof being provided with a tool receiving surface.

UNITED STATES PATENTS Paige Aug. 20, 1929 Marshall Feb. 14, 1933 SpencerSept. 4, 1934 Bletz et al. Sept. 24, 1935 Bolesky May 7 1940 Evans Apr.22, 1941 Butler May 23, 1950

